1. Statement of the Technical Field
The present invention relates to providing power to peripheral devices, and more particularly to providing power to a device such as a wireless transmitter using a data communications signal line that is not always active.
2. Description of the Related Art
While new devices and buses such as the Universal Serial Bus (“USB”) include provisions for providing power to remotely connected peripheral devices, there is a very large body of technologies and deployed equipment that provide interfaces for serial communication to remote devices that do not include provisions for providing power. Many serial interface technologies, such as RS-485 and RS-422 interfaces, were historically used for programming or configuration access by service personnel, or hard wired to centralized systems. However, it is desirable to be able to use these interfaces to allow transmission for remote telemetry or configuration without the need for hard wired retrofitting, such as through the use of low power, low data rate radio communications.
In addition, it is also possible that existing installations that are to be retrofitted to allow remote communication using devices such as radios do not include additional power outlets, or make other provisions for providing external power. Even for new installations, adding outlets to power peripheral devices such as radios adds to the cost of installation as well as the time needed to install the outlets or otherwise run power to installation location.
Many types of serial interfaces, such as RS-485 and RS-422 interfaces, do not provide for powering devices coupled to the interface. In large part this is because such interfaces operate in a differential mode are maintained in a high impedance un-powered state when the interface is inactive. As such, power can not be provided to a connected peripheral device via the serial interface and, as noted above, the remote device must be powered by running a separate power line from another source, using a battery, etc.
By way of a specific and practical example, many electronic article surveillance systems have sensors and deactivators that are interconnected or configured via RS-485 interfaces. Installations can more easily be completed if remote communications can be accomplished wirelessly using low power low data rate radios. Also, expanding existing installations is greatly simplified if radios that are powered by the deactivators or sensors themselves can be used rather than running additional wire and power to the installation location. For example, consider how much less expensive and less disruptive it would be to add an additional cash register lane at a retail store if the deactivator could communicate with the central processing unit using a wireless communication link in a manner that did not impose an additional power receptacle or battery burden. It is therefore desirable to have an arrangement that allows interfaces that are typically un-powered when inactive to provide power to an interconnected device.